The most varied constructional embodiments of such a process are disclosed by the prior art. According to these on a correspondingly .large, previously prepared open air surface, lawns are sown and cultivated in the usual way until a strong sward has formed. The finished law is then mechanically cut up into widths, rolled up and transported to the final place of use. Such roll-type lawns or manually cut turfs are unsatisfactory in a number of respects.
Firstly the manual cutting is imprecise and in the marginal areas leads to faults and non-uniform joints. Secondly damage occurs during transportation and storage as a result of compressive loading and the exclusion of air in the rolled-up state, which causes a significant amount of damage after a few days. Thirdly it is particularly disadvantage that it is not possible in this way to produce, transport and lay in a continuous support-free manner intensively rooting plant types, such as e.g. succulent species (sedum). In fact, they extremely easily break apart. Thus, according to DE-A-1 801 460 a web-like, cut-through plastic support material is required for rolled-up lawns. The recent literature also requires for this purpose the most varied support materials.
In the book "Grundlagen der Dachbegrunung" by Liesecke et al, 1989, in chapter 10"Greening processes and care" under 10.1.4, the prior art of vegetation mats is described.
The guidelines for roof greening of the Forschungdgeselolschaft Landschaftsentwicklung Landschaftsbau (FLL), 1990 edition constitutes the authoritative work in the field of roof greening and represents the up-to-date prior art. It is stated therein under 10.2.7 vegetation mats: "For cultivation, transportation, laying and use purposes, vegetation mats must comprise suitable support inserts . . . "
In the book "Dachbegrunung" by Bernd Krupka in the series Handbuch des Landschaftsbaus, Eugen Ulmer Verlag, 1992, vegetation mats are discussed in section 16.3.
All three of the above publications give a detailed description of vegetation mats. According to these, the prior art characterizes a vegetation mat in that it has a support or carrier insert for cultivation, transportation and laying purposes.
It is also required e.g. in DE-C-38 05 069, that a watering and draining mat for a vegetation element has a support layer of mechanically stabilized polyester needle-punched web, in order to counteract a serious wetting risk.
All the known vegetation mats have straw, coconut and nonwoven matting as the support, said mats being rottable, whereas so-called claw fabric mats fulfilling the same function are resistant to rotting and tension-proof. The main function of the rottable support inserts is to render said vegetation mats transportable, so that after cultivation they can be rolled up, loaded onto Euro-pallets and e.g. laid by simply rolling out in extreme positions such as roofs, as well as on salt, coal or refuse heaps. Whereas the rottable support inserts lose their function after rotting, the claw fabric mats have to retain certain functions. The conventional vegetation mats provided with supports are disadvantageous in several respects. Thus, they are cultivated or grown on a plastic sheet or the like, which becomes unusable after it has been used for one or two growing processes and must be disposed of at high cost. Due to the contamination of the plastic sheet recycling is not at present possible. In order that they have a sufficiently high strength for one to two years, the rottable support layers must have a non-rottable plastic fraction of up to 30% in the form of plastic fibres or fabrics. In the case of so-called nonwoven mats there are wind and water erosion problems during cultivation, particularly at the edges, because the vegetation mat substrate is merely placed on the nonwoven and not, as is the case with claw fabric mats, intermeshed with the support. If nonwoven mats are e.g. laid on the roof, but the transportation has led to the dropping out of vegetation parts or substrate which have not been repaired, in these areas there is an increased susceptibility to wind and water erosion. At these points the nonwoven is exposed. Thus, so-called "bald patches" are formed, which are virtually non-colonized by vegetation and a closing of the vegetation is only possible as a result of significant effort and expenditure.